1. Field of the Invention
The present invention relates to a display element and a method of manufacturing a display element, and particularly, to a display element capable of efficiently emitting generated light externally and a method of manufacturing the display element.
2. Description of the Related Art
Conventionally, in the case of display elements which use, for example, an organic electroluminescent element or the like as a light emitting element, the organic electroluminescent element is typically formed over a glass substrate. FIGS. 2A to 2C are explanatory diagrams showing constructions and operations of a conventional display element. FIG. 2A is an explanatory diagram showing an example construction of a first conventional element. Note, however, that in the diagram, each layer is depicted in an exaggerated fashion and differs from actual relative proportions.
The EL (electroluminescent) elements referred to in this specification include triplet-based light emission elements and/or singlet-based light emission devices, for example.
The conventional sequence for forming the film coating is to sputter a transparent electrode 31 (e.g., ITO: indium oxide-tin oxide alloy) on a glass substrate 30, and then an organic electroluminescent layer 32 is formed by vapor deposition or by spin coating onto the substrate 31, and a cathode 33 is evaporated. After that, sealing material 34 is used to adhere a facing substrate 35 to prevent deterioration of the organic electroluminescent layer 32 and the cathode 33 due to the atmosphere.
FIG. 2B is an explanatory diagram showing an optical path in the first conventional example element. In the above-mentioned conventional structure the cathode material of the cathode 33 is a metal. Therefore, light emerges from the substrate 30 side (FIG. 2B, optical path A), but, due to differences in the refraction indices of each of the layers, the light cannot escape from the front surface of the element at a angle greater than the critical angle (FIG. 2B, optical paths B and C). Therefore, the emergence ratio of the light is 1/(2n2); where n is the refraction index of the luminous layer 32 (approximately 1.6). Therefore, there was a problem that 80% of the light generated was guided inside the glass substrate 30 and escaped sideways.
In order to avoid this problem, a method has been proposed for forming the film coating on the glass substrate in the reverse sequence starting with the cathode. FIG. 2C is an explanatory diagram showing a structure of a second conventional example element. The sequence for forming the film coatings was, first, to vapor deposit a cathode 36 on the glass substrate 30. Then, after vapor depositing or spin coating an organic electroluminescent layer 37 for film coating, a transparent electrode 38 such as that of ITO was formed by sputtering. In this case it was necessary to sputter a transparent conducting film 38 such as that of ITO onto the electroluminescent film 37, but there was a problem that the organic electroluminescent layer 37 was altered due to damage suffered and increased temperature experienced during sputtering.